Level transmitters that transmit and receive reflected electromagnetic pulses along a waveguide in a container are known. These level transmitters provide one or more local or remote outputs that indicate a fluid level in the container.
The fluid level in a storage container, and also the transmitter outputs can remain unchanged for long periods of time. An operator may not be able to tell the difference between an unchanging transmitter output that accurately indicates an unchanging fluid level and an unchanging transmitter output that is stuck at a fixed output value because the waveguide or level transmitter is malfunctioning. A localized build-up of contamination on the waveguide, for example, can cause such a malfunction. If a level output is stuck, then fluid can be lost from the container, or the container can be overfilled, without any warning to the operator.
A method and an apparatus are needed to enable an operator to reliably ascertain whether an unchanging level transmitter output is due to an unchanging level or due to a malfunction.